Many displays include an array of pixels organized in rows and columns. Selecting a row and selecting a column enables addressing of a pixel in the array. There are two categories of addressing schemes. One is referred to as a passive matrix addressing scheme in which the row and column drivers are multiplexed to turn pixels on and off in the array. Another addressing is referred to as an active matrix addressing scheme in which one or more thin film transistors (“TFT”) is associated with each of the pixels in the display to turn the pixel on and off. Generally, the displays that use a passive addressing scheme are referred to as passive displays and the displays that use an active addressing scheme are referred to as active displays.
Currently, both passive and active displays have data reside in an external memory. In other words, the memory is remote from the pixel. The data is sent to the pixels via rows and columns in the form of voltage pulses. As a result, the pixels are refreshed for both the passive displays and the active displays. The refresh rates are high and expected to increase as displays become more complex. For example, high definition television (“HDTV”) uses a display having an array of pixels of 1080×1920. The refresh rate of the entire image is generally between 60-90 frames per second. As the number of rows increase, the amount of time that may be spent addressing each row becomes shorter because memory is remote from the pixel. Static or quasi-static display applications even have high refresh rates.
Although in principal passive displays appear to be easier to fabricate, complex schemes are implemented in order to address each pixel. In a large display, such as an HDTV display, as the number of rows and number of columns increase, the time available to address each pixel becomes shorter. If a display is a liquid crystal display, the response time for such programming is slow enough so that, eventually, the pixel does not respond well and contrast between on and off pixels is poor. If a display is an OLED display, the brightness of each pixel is increased in proportion to the number of rows in the display, since rows are activated one at a time. Consequently, large current densities are used in passive OLED displays, leading to high power consumption.
Active displays include one or more TFTs to address each pixel and generally are much more difficult to fabricate. The difficulty in fabrication translates to expense passed on to consumers. In some instances, the cost may be prohibitive for many consumers. The active displays also use a glass substrate. Complex processes are also generally used to fabricate an active matrix display.